Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$36.66	4.543%	$38.3255	$38.33	$38.35	$38.30
Purchase #2	$108.54	13.524%	$123.2189	$123.22	$123.20	$123.20
Purchase #3	$126.47	5.642%	$133.6054	$133.61	$133.60	$133.60
Purchase #4	$177.38	10.853%	$196.6311	$196.63	$196.65	$196.60
Purchase #5	$92.52	6.214%	$98.2692	$98.27	$98.25	$98.30
Purchase #6	$134.35	10.866%	$148.9485	$148.95	$148.95	$148.90
Purchase #7	$230.90	9.392%	$252.5861	$252.59	$252.60	$252.60
7 purchase totals =	$906.82		$991.5847	$991.60	$991.60	$991.50